LINEAR AND NONLINEAR DYNAMICS OF HEART-RATE-VARIABILITY AFTER ACUTE MYOCARDIAL INFARCTION WITH NORMAL AND REDUCED LEFT-VENTRICULAR EJECTIONFRACTION

We analyzed heart rate variability (HRV) in 2 groups of patients after acute myocardial infarction with normal and reduced ejection fraction (EF) by considering both the power of the 2 major harmonic components at low and high frequency and 2 indexes of nonlinear dynamics, namely the 1/f slope and the correlation dimension D-2. HRV of patients with a reduced EF was characterized by a diminished RR variance as well as a different distribution of the residual power in all frequency range s, with lower values of the low-frequency component expressed in both absolute and normalized units, and of the low- to high-frequency ratio . In these patients we also observed a steeper slope of the negative r egression line between power and frequency in the very low frequency r ange. The presence of a smaller fractal dimension was suggested by a l ower D-2. Thus, in patients after acute myocardial infarction with a r educed EF, the reduction in HRV is associated with a different distrib ution of the residual power in the entire frequency range, which sugge sts a diminished responsiveness of sinus node to neural modulatory inp uts.